All speculation on future games can be held in the official thread: http://www.gamesas.com/topic/1511589-official-beyond-skyrim-tes-vi-47/
But no, Argonia is nothing more than a rumour from a few years ago that someone spent a lot of time on. Unless you hear it from Bethesda, consider it false
Bethblog.com is the best source for all current Bethesda news.